Conventional display devices perform screen refreshing at constant cycles (e.g., 60 Hz) even when displaying images which barely change, such as still images, on the screens, and therefore it is difficult to reduce their power consumption.
FIG. 14 is a diagram illustrating a conventional relationship between a host processor 90 (referred to below as a “host 90”) and a display device 80. As shown in FIG. 14, the host 90 transmits video data and a mode-switching signal to the display device 80, and the display device 80 displays an image after switching the mode in which to perform screen refreshing on the basis of the received mode-switching signal. In response to the mode-switching signal, the display device 80 selects the cycle at which to perform screen refreshing from among a plurality of preset frequencies. For example, when there are preset selectable refresh modes A and B at 60 Hz and 30 Hz, respectively, the screen refreshing is performed either in mode A or B in accordance with the mode-switching signal transmitted by the host 90. In this manner, by performing screen refreshing while appropriately switching between modes A and B, it is rendered possible to reduce power consumption by the display device 80 compared to the case where screen refreshing is always performed in mode A.
Furthermore, Japanese Laid-Open Patent Publication No. 2002-207462 discloses a liquid crystal display device capable of reducing power consumption in displaying a still image. In this liquid crystal display device, a drive idle period is set to keep a driver circuit idle and maintain potentials of scanning lines and signal lines at fixed levels before transition from one frame to another. As a result, the liquid crystal display device can reduce power consumption in displaying a still image.